The last few years have witnessed the introduction of optical (and electrical) mesh networks as an alternative to synchronous optical network-based (SONET-based) ring networks. One of the key benefits of mesh networks is the improved bandwidth utilization coming from path diversity and shared restoration. Unlike the traditional 1+1 protection technique which reserves 50 percent of the bandwidth for backup paths, shared restoration allows multiple demands to share backup channels and hence reserves less capacity.
However, shared restoration comes at the cost of increased restoration times. Industry standards demand that circuits at the transmission layer be restored within, for example, 50 milliseconds in order to support voice and other SONET traffic. This is easy to achieve with 1+1 protection because traffic is simply switched to a pre-setup backup path on failure and operations resume almost instantaneously. Under shared restoration, since a backup channel may belong to multiple paths, it is not possible to set up the backup paths a priori. Instead, the path is precomputed, but set up after a failure. Set up involves signaling, acknowledgments, and cross connect configurations. This typically takes much longer than the required 50 milliseconds, making the technique non-viable for many applications.
Motivated by these and other deficiencies, a fast shared restoration technique was proposed in the U.S. patent application identified as Ser. No. 10/392,574, entitled “Low Latency Shared Data Path Allocation,” filed Mar. 20, 2003 and commonly assigned; and also in C. Phadke et al., “FASTeR: Shared restoration without signaling,” OFC, Mar. 2003, the disclosures of which are both incorporated by reference herein. In accordance with the fast shared restoration technique, if the degrees of a shared channel (i.e., the number of shared channels incident on that channel at its ends) are restricted to a finite number (K), then one can in fact pre-establish the backup paths and restore them almost as fast as 1+1 protection. Networks implementing this fast shared restoration technique are referred to as K-shared networks. However, traditional routing and design algorithms may not always work efficiently with networks implementing such a fast shared restoration technique.
Thus, a need exists for routing and design methodologies for use with networks implementing such a fast shared restoration technique and the like.